1. Field of the Invention
The present invention relates to lead frames and the manufacturing method thereof, and more particularly, to a lead frame in which the inner leads of the leads connect to electrodes of a semiconductor chip and the outer leads of the leads connect to electrodes of a printed circuit board or the like through protruding electrodes and the manufacturing method thereof.
2. Description of the Related Art
An example of a connection between a semiconductor chip and a printed circuit board or the like through an organic substrate having protruding electrodes such as solder balls is disclosed in U.S. Pat. No. 5,136,366. The structure of this conventional example will be described below by referring to its cross section shown in FIG. 1.
In FIG. 1, a semiconductor chip xe2x80x9cbxe2x80x9d is mounted on a surface of a multilayer organic wiring substrate xe2x80x9caxe2x80x9d having about two to six layers and using an organic material. Wiring film xe2x80x9ccxe2x80x9d formed on the surface of the substrate xe2x80x9caxe2x80x9d is connected to electrodes of the semiconductor chip xe2x80x9cbxe2x80x9d through connection wires xe2x80x9cdxe2x80x9d made of gold or the like.
Solder balls xe2x80x9cexe2x80x9d formed on the opposite surface of the substrate xe2x80x9caxe2x80x9d are electrically connected to the wiring film xe2x80x9ccxe2x80x9d via through holes. There is also shown solder resist film xe2x80x9cf,xe2x80x9d sealing resin xe2x80x9cg,xe2x80x9d and a printed circuit board xe2x80x9ch.xe2x80x9d
In the conventional example shown in FIG. 1, the multilayer organic wiring substrate xe2x80x9caxe2x80x9d with which the semiconductor chip xe2x80x9cbxe2x80x9d is mounted and resin-sealed on the main surface and the solder balls xe2x80x9cexe2x80x9d serving as protruding electrodes are formed on the other surface is connected to the printed circuit board xe2x80x9chxe2x80x9d with the solder balls xe2x80x9ce.xe2x80x9d
Since electrodes of the semiconductor chip xe2x80x9cbxe2x80x9d are connected to the wiring film xe2x80x9ccxe2x80x9d on the multilayer organic wiring substrate xe2x80x9caxe2x80x9d called BGA through the connection wires xe2x80x9cd,xe2x80x9d made of gold or the like, parasitic resistance inevitably becomes large. In addition, a wire-bonding process is required, which requires time which cannot be ignored, thus being a factor for increasing cost.
Since the semiconductor chip xe2x80x9cbxe2x80x9d is mounted and resin-sealed on the main surface of the substrate xe2x80x9ca,xe2x80x9d it is difficult to respond to an increasing demand for making semiconductor devices thinner.
There are also other drawbacks related to the multilayer organic wiring substrate xe2x80x9ca.xe2x80x9d These are a very high manufacturing cost due to the complicated manufacturing process, a high defect rate which cannot be ignored due to its tendency to generate warps, and a probability of water invasion from the side faces of the substrate.
Accordingly, it is an object of the present invention to provide a highly reliable lead frame and the manufacturing method thereof which respond to a demand for making semiconductor devices thinner and more inexpensive.
The foregoing object is achieved according to one aspect of this invention through the provision of a lead frame wherein a number of leads having their inner leads extending over a device hole are connected to electrodes of a semiconductor chip and their outer leads are connected to protruding electrodes are formed on a surface of protective insulation film having the device hole, the outer leads being provided with the protruding electrodes on the surface opposite the surface which is closer to the protective insulation film.
In the lead frame, a reinforcement plate may be formed on the surface opposite the surface of the protective insulation film on which the leads are formed.
The foregoing object is achieved according to another aspect of the present invention through the provision of a manufacturing method of the lead frame, comprising the processes of: forming a number of leads on an etching stopper layer above a surface of a lead-forming substrate; adhering the protective insulation film having the device hole on the surface of the leads opposite the surface closer to the lead-forming substrate; eliminating areas of the lead-forming substrate used for forming the leads by etching from the rear side; and forming the protruding electrodes on the outer leads of the leads.
The foregoing object is achieved according to still another aspect of the present invention through the-provision of a manufacturing method of the lead frame, comprising the processes of: forming a number of leads on an etching stopper layer above a surface of a lead-forming substrate; half-etching the rear surface of the lead-forming substrate corresponding to lead-forming areas; forming a solder resist having openings at positions where the protruding electrodes are to be formed, on the lead-forming surface of the lead-forming substrate; forming the protruding electrodes on the leads with the electrolytic plating method using the solder resist as a mask; etching the remaining areas on the rear surface of the lead-forming substrate corresponding to the lead-forming areas; and adhering the protective insulation film having the device hole on the surface of the leads opposite the surface on which the protruding electrodes are formed.
The foregoing object is also achieved according to a further aspect of this invention through the provision of a lead frame wherein a solder resist having openings for exposing outer leads is formed on one surface of a number of leads and protruding electrodes are formed at the exposed outer leads.
The foregoing object is achieved according to a still further aspect of this invention through the provision of a manufacturing method of the lead frame, comprising the processes of: forming a number of leads on an etching stopper layer above a surface of a lead-forming substrate; forming a solder resist having openings at positions where the protruding electrodes are to be formed, on the lead-forming surface of the lead-forming substrate; forming the protruding electrodes on the leads with the electrolytic plating method using the solder resist as a mask; and etching the remaining areas on the rear surface of the lead-forming substrate corresponding to the lead-forming areas.
With the-above-described structure, the leads comprising the single-layer wiring film formed on the surface of the protective insulation film intervene between electrodes of the semiconductor chip and protruding electrodes, instead of using a multilayer organic wiring substrate, reducing the cost. In addition, since the leads have a single layer, water cannot invade between layers, increasing humidity-proofness and water-proofness. By placing a semiconductor chip in the device hole, which is provided for the protective insulation film, the semiconductor device can be made thinner.
Since the reinforcement plate is adhered to the rear surface of the protective insulation film, the lead frame is effectively prevented from being deformed and broken in the manufacturing process of the lead frame, and the mounting and resin-sealing processes of the semiconductor chip.
With a manufacturing method for the lead frame according to the present invention, since the leads are formed on the etching stopper layer above the lead-forming substrate, the leads can be made fine and they are prevented from being deformed in manufacturing even if they are thin because the lead-forming substrate functions as a support. Since the protective insulation film or the multilayer member comprising the protective insulation film and the reinforcement plate is formed on the leads, which are prevented from being deformed by the lead-forming substrate, the leads 3 are prevented from being deformed in forming processes such as that for the protective insulation film.
With a manufacturing method according to the present invention, since the etching stopper layer is made from an electrically conductive material and the protruding electrodes are formed before the process for etching the etching stopper layer, with the leads being used as masks, the etching stopper layer can be used as a path for applying the voltage required for electrolytic plating the portions where the protruding electrodes are to be formed, therefore enabling the protruding electrodes to be formed in electrolytic plating. This means that a process for placing the material for the protruding electrodes at positions where the protruding electrodes are to be formed is not necessary, making work for forming the protruding electrodes highly efficient and thus reducing the manufacturing cost.
Since the protective insulation film or the multilayer member comprising the protective insulation film and the reinforcement plate is formed on the leads after the etching stopper layer is etched, with the leads being used as masks, the protective insulation film and other components prevent the leads from being deformed in the inner-lead bonding and resin-sealing processes. In addition, since the leads have a single layer, water cannot invade between layers, increasing humidity-proofness and water-proofness, thus increasing reliability.
In a lead frame according to the present invention, instead of a multilayer, organic wiring substrate, the single-layer lead having the protective insulation film at the front surface is used and placed between the electrodes of the semiconductor chip and the protruding electrodes, reducing the cost.
With a manufacturing method according to the present invention, since the semiconductor chip is resin-sealed after inner-lead bonding, the positions of the leads and the positional relationship between the leads are fixed to the semiconductor chip with the sealing resin.
Since the etching stopper layer is made from an electrically conductive material and the etching stopper layer is etched, with the leads being used as masks, the etching stopper layer can be used as a path for applying the voltage required for electrolytic plating the portions where the protruding electrodes are to be formed, therefore enabling the protruding electrodes to be formed in electrolytic plating. This means that a process for dropping the material for the protruding electrodes at positions where the protruding electrodes are to be formed is not necessary, making work for forming the protruding electrodes highly efficient and thus reducing the manufacturing cost.